1. Field of the Invention
The present invention relates to a melanin decomposing method comprising using a microorganism, especially a species of Basidiomycetes having melanin decomposing potency. The present invention also relates to a melanin decomposing substance and a whitening cosmetic.
2. Description of the Related Art
Melanin is biologically synthesized in central nerve and retina in addition to skin in animals and is further present in widespread manner in nature from plants to microorganisms. Melanin is synthesized as follows; firstly, the precursor tyrosine is transformed into a second precursor dopa and then a subsequent precursor dopa-quinone via the action of tyrosinase, and is further oxidized into the precursor indole-5,6-dihydroquinone, which is then polymerized into melanin (Protein, Nucleic Acid and Enzyme, Vol.15, pp.550 (1970)). As utilized herein the term "precursor" includes tyrosine, dopa, dopa-quinone and indole-5,6-dihydroquinone, all of which are known precursors in the biological synthesis of melanin.
Melanin is synthesized in melanocytes, cells present in the epidermal basal layer,the reaction thereof is stimulated by ultraviolet ray (often referred to as UV ray hereinafter) (Ryo-ichi Fukushiro et al., "Diagnostics and Therapy in Dermatology; Vol.4", Kodansha Press, pp.38). In melanocyte, melanin is synthesized and matured in the granules referred to as melanosome. Subsequently, melanin migrates to epidermal cells and is then dispersed therein, where melanin is decolored following dermal metabolism and then scaled off in the form of dirt at the time of the renewal (Cell, 4, (9), P.16(1972)). As has been described above, melanin is a factor of clinical importance, because it is responsible for a significant function for protecting physical bodies against adverse effects of UV ray. However, a higher level of melanin causes darker skin. Furthermore, the heterogeneous distribution thereof causes chloasma and freckling, involving serious problems in terms of beauty.
Hitherto known countermeasures against chloasma and freckling are broadly classified in two preventive methods and one therapeutic treatment.
The following methods have been known as such preventive methods;
1.) a method for shielding skin from UV ray which triggers melanin biosynthesis via sun screening agents and the like ("Recent Science of Cosmetics", Cosmetic Science Research Group eds., Yakuji Nippo Corporation (1986)); and 2.) a method comprising using melanin biosynthesis-inhibiting pharmaceutical agents, for example, melanin synthesis-inhibiting agents such as glutathione, vitamin C, cysteine, arbutin and sodium thiosulfate (Japanese Patent Laid-open Nos. Sho. 53-142515 and Sho. 48-44442).
Presently, however, no safe method without side effects has been developed yet so as to therapeutically treat and eliminate chloasma and freckles once formed (Ryo-ichi Fukushiro et al., "Diagnostics and Therapy in Dermatology; Vol.4", Kodansha Press, pp.38; Jun-ichi Miyazaki, "External Preparation for Skin; Preparative method and Application", Nanzando Press, pp.273-275, 353-355). As a bleaching agent for skin, hydroquinone, 4-isopropylcatechol, and hydroquinone monobenzyl ether and the like have been made use of in the past, but because of their strong whitening action based on the degeneration and death of pigment cells, their continuous external application possibly may cause eternal leucoderma, unavoidably involving side effects such as dyschromatosis and rash. Therefore, the development of a safe pharmaceutical agent for treating chloasma and freckle has been expected earnestly in the industry (Japanese Journal of Clinical Dermatology, 44, (6), pp.629 (1990)).
It is known to treat freckles by shortening the period in which melanin is scaled off following epidermal metabolism. This is accomplished by using agents to soften and peel off the keratin. Typical agents are resorcin and salicylic acid. One such method for therapeutically treating chloasma and freckles is described by Jun-ichi Miyazaki, "External Preparation for Skin; Preparative Method and Application", Nanzando Press, pp. 273-275, 353-355. However, these methods cannot be regarded as a method for essentially treating chloasma and freckle; and the methods require a long period of time lasting several months for the treatment, which cannot be said as a practical therapy.